U.S. Pat. No. 4,134,107 issued Jan. 9, 1979 for an invention of Miller et al. entitled "Replacement Elevator Call Button Assembly" discloses a direct replacement unit for an Otis Elevator touch button assembly. Series-connected zener diodes are used to drop the voltage across the power supply lines which couple the call button assembly to the Otis Elevator controller. The voltage drop is equivalent to that sustained by an original equipment Otis Elevator gas tube type elevator call button assembly, thereby allowing the Miller et al. device to serve as a direct replacement for an original equipment Otis Elevator touch button assembly.
Although the Miller et al. device offers a number of advantages over the original equipment Otis Elevator touch button assembly, it has some inherent disadvantages. For example, in buildings equipped with multiple elevator shafts, more than one elevator call button assembly may be provided on each floor of the building. This allows ready access to the call buttons by any one who wants an elevator car to stop for passengers at a particular floor. Conventionally, if someone presses an elevator call button on a particular floor, then that call button is illuminated to indicate that an elevator has been called; and, all corresponding buttons in any other call assemblies provided on the same floor are simultaneously illuminated. Waiting passengers are thus informed that no further call buttons need be pressed to summon an elevator to that floor.
The simultaneous illumination of the additional call buttons is accomplished by a technique called "cross firing". In the original equipment Otis Elevator touch button assembly, cross firing between the call assemblies located on a particular floor is achieved by applying a negative bias voltage to the triggers of each of the glass tube touch buttons provided on that floor, and by wiring the cathodes of each button together. When an individual touches one of the tubes, that tube fires, thereby activating the Otis Elevator controller and illuminating the touched tube to indicate that an elevator has been summoned. The negative bias trigger voltage and the cathode interconnections to the remaining tubes cause breakdown to occur between the cathodes and triggers of the remaining tubes. This in turn results in further breakdown between the anodes and cathodes of the remaining tubes, thus firing (i.e. illuminating) the remaining tubes.
In order to achieve cross firing, the Miller et al. device requires additional wires to be run between the elevator call button assemblies located on the particular floor at which cross firing is desired. Such additional wiring can be an expensive, time-consuming, laborious operation in view of the fact that the Miller et al. device is primarily intended to replace previously installed Otis Elevator touch button assemblies (i.e. workmen must gain access to the ceilings and walls adjacent the elevator shafts in order to install the additional wiring).
The present invention is also capable of serving as a direct replacement for an Otis Elevator touch button assembly, or as a direct replacement for equivalent assemblies such as the Miller et al device. Unlike the prior art replacement assemblies, the present invention requires no additional wiring in order to achieve cross firing at floors equipped with two or more elevator call button assemblies.